The invention relates to an apparatus and method for obtaining uniform gobs in a triple gob feeder of a molten glass forming apparatus, and more particularly for obtaining uniform gobs by providing uniform molten glass temperatures in a triple gob orifice ring.
In a common commercial process for the production of glass containers, such as bottles, jars and the like, and other types of glassware, glass components are initially heated to an elevated temperature level, such as 2000.degree. to 2100.degree. F., in a forehearth to form a relatively uniform mass of molten glass. The molten glass is fed to a spout bowl having a glass discharge hole in a central portion of the bottom wall of the bowl. A tube is provided in the spout bowl having a diameter slightly larger than the discharge hole and adapted to engage the bottom wall of the spout bowl surrounding the glass discharge hole. The tube is raised and lowered to regulate the flow of molten glass in the spout bowl through the discharge hole. The molten glass is then received by and temporarily stored in an orifice ring positioned immediately below the discharge hole of the spout bowl. Molten glass in the orifice ring is urged through orifices in the orifice ring at regular intervals by reciprocating plungers mounted above the orifice ring in axial alignment with the orifices. As the molten glass flows through the orifices, it is formed into a continuous rod-like body of glass which is cut by shears mounted below the orifice ring into discrete units of desired size, referred to as "gobs". Commonly used orifice rings have one, two or three orifices (referred to as "single gob", "double gob" or "triple gob" orifice rings, respectively) to simultaneously produce one, two or three gobs. Prior examples of triple gob orifice rings are disclosed in U.S. Pat. No. 3,516,812 and U.S. Design Pat. No. De. 241,269. The gobs produced by the foregoing process are then fed to additional glass forming apparatus to be formed into the desired article.
In the commercial application of the foregoing process, uniformity of the size and shape of gobs produced is critical not only to ensure production of a uniform, quality article, but also to minimize use of excess glass while ensuring sufficient glass in the gob to produce a minimum wall thickness in a container, such as a bottle. The size and shape of gobs produced is highly dependent on the viscosity of the molten glass in the orifice ring and therefore upon the temperature of the glass flowing through the ring orifices. It has been found that it is particularly difficult to maintain uniform temperatures of glass flowing through the orifices of a conventional triple gob orifice ring having three orifices oriented in the ring with orifice centers in substantially linear alignment forming two end orifices located adjacent the sides of the orifice ring and a middle orifice located in a central portion of the orifice ring. With such an arrangement, molten glass adjacent the end orifices is cooled relatively more than molten glass adjacent the middle orifice due to the proximity of the end orifices to the sides of the orifice ring. Presently used designs additionally pack more insulation around a middle reservoir supplying molten glass to the middle orifice than end reservoirs supplying molten glass to the end orifices, thereby compounding the problem. With a relatively higher temperature of molten glass adjacent the middle orifice, the glass flowing through that orifice tends to have a relatively lower viscosity resulting in the production of gobs from the middle orifice of relatively higher glass content and elongated shape. Some prior art triple gob orifice rings further increase the problems of uniform gob production by utilizing orifices of uneven wall height.
It has now been found that the foregoing problems can be overcome and gobs of uniform size, weight, volume and shape can be produced in a triple gob feeder, by equalizing the temperatures of the molten glass flowing through a triple gob orifice ring by retaining molten glass in a middle molten glass reservoir of the orifice ring for a relatively longer average period of time than in end reservoirs of the ring, and, preferably, by additionally cooling the middle reservoir of the ring. The uniformity of gobs produced may be further improved by providing orifices in the ring having a uniform height.